The most frequent cause of visual loss in childhood is functional amblyopia. Recent studies show that a high spatial frequencies and under conditions of crowding, qualitatively different acuity losses are found in different amblyopes. The present proposal will capitalize on these differences as a means of clarifying the specific losses in peripheral vision and amblyopic vision compared to normal foveal vision. Just as color deficient individuals had contributed much to our knowledge of color vision, we expect amblyopes will contribute much to our knowledge of spatial vision. Several new psychophysics methodologies will be used to help unravel the comples story: 1. There is a golden opportunity to learn about the amblyopic distortion by comparing the amblyopic eye to the nonamblyopic eye. Under the proper conditions, amblyopes (even those with anomalous correspondence) can not determine the eye-of-origin of a stimulus. By using a double judgment methodology, eye-of-origin confusions will be used to convert subjective interocular comparisons into objective signal detection measurements. New methods for analyzing double judgment tasks with the effects of response bias and response correlation minimized will be used to extend signal detection methodology to the suprathreshold regime. The proposed experiments will focus upon the interactions between local features in peripheral as well as amblyopic vision: 1-Repetitive arrays of features will allow apatial frequency analysis to be used. Spatial frequencies within 3/2 octave of the cutoff spatial frequency will be exhaustively investigated. Effects of phase and background contrast will be explored. 2-A hierarchy of localized luminance distributions will be used to measure contrast sensitivity and phase sensitivity will be studied in amblyopes and peripheral vision. 3. After the first year, nonlocal phase effects, effects of crowding and two dimensional stimuli (ie vernier acuity) will be studies. 4. Quantitative modelling will be used to explain amblyopic and peripheral losses in terms of underlying mechanisms.